of toxicity of the dispersant versus the relative toxicity of the spilled oil, to ensure that dispersant use mitigates an oil spill rather than making the problem worse. Corexit products have been used in oil spill response activities since the late 1960s. Early products in the line included Corexit 7664 and Corexit 8666. Corexit 9527 is one of the first modern concentrate dispersants and has been in use since the mid 1970s. Corexit 9500 was designed to replace Corexit 9527. In 2002, Corexit 9527 and Corexit 9500 were the only two chemical dispersants stockpiled in large quantities in the U.S.A. An estimated 2.5 million gallons of chemicals were used in response to the supertanker SS Torrey Canyon oil spill in the United Kingdom in 1967. The incident harmed marine life and triggered the first significant international public discussions about chemical dispersants' toxicity including the costs and benefits of its deployment. 1968–1988 In April 1968, 300 barrels of Corexit were shipped to the scene of the stricken tanker Esso Essen off the African coast. 125 barrels of it was sprayed onto the slick by aircraft over two days, after which the slick was dispersed. Corexit was later used in response to the sinking of the Greek tanker Andron off the west African coast. Following these events, Humble Oil and Refining Co. and the Enjay Chemical Company (a subsidiary of the Standard Oil Company of New Jersey) each announced the development of Corexit 7664, describing it as non-toxic to marine life- even to shrimp at concentrations of 1% per volume of seawater. Ecotoxicological studies had been undertaken by the Institute of Marine Science at the University of Miami. Corexit 7664's point of difference was described by research chemist Dr Edward Corino to be its water base, where previous dispersants had been hydrocarbon-based and highly toxic. James Avery, Humble Oil and Refining Company's public relations representative for the eastern region confirmed that following the Torrey Canyon oil spill, another spill in the Fore River from a tanker en route to Weymouth, south of Boston hastened Corexit 7664's development. In February 1969, following application tests in Montreal, Quebec, Canada, the Imperial Oil company announced that it had equipped its fleet of tankers and barges with Corexit for the purpose of dispersing oil spills. In February 1970, Corexit was deployed by aircraft onto an oil slick leaking from the stricken tanker Arrow in Nova Scotia,